A known substrate for mounting electronic components and a known electronic apparatus including the substrate are described with reference to FIGS. 7A to 9. A known wiring board 1 for mounting electronic components such as semiconductor devices and piezoelectric vibrators is usually made of a ceramic material having a substantially rectangular shape and includes an insulating base 2 having an electronic component-mounting portion 4 in its upper face, a plurality of wiring layers 3 extending from the electronic component-mounting portion 4 of the insulating base 2 to the side surfaces through the interior of the insulating base, a plurality of connecting pads 5 formed on the peripheral portion of the lower surface of the insulating base 2, and a plurality of groove-shaped recesses 6 which are formed in side surfaces of the insulating base 2, which have conductors 7 adhered to the inner wall surfaces, and which electrically connect the wiring layers 3 to the connecting pads 5 through the conductors 7. An electronic apparatus 10 is made by mounting an electronic component such as a semiconductor device 11 on the electronic component-mounting portion 4 of the insulating base 2, electrically connecting electrodes such as signal and ground electrodes of the electronic component to the wiring layers 3 via conductive connecting members such as bonding wires 12, and then bonding a metal lid 13 composed of an iron-nickel-cobalt alloy, an iron-nickel alloy, or the like or a lid 13 composed of a light-transmitting material such as glass on the upper surface of the insulating base 2 by using a blazing material, an adhesive, or the like so as to cover and seal the electronic component.
The electronic apparatus 10 is mounted on an external electrical circuit board 20 by connecting the connecting pads 5 formed on the peripheral portion of the lower surface of the insulating base 2 to lead conductors 21 of the external electrical circuit board 20 by using a solder 31 such as a tin-lead solder or the like. Meanwhile, each of the electrodes of the electronic component is electrically connected to the external electrical circuit via the connecting pad 5, the conductor 7 on the internal wall surface of the groove-shaped recess 6, and the wiring layer 3. During this process, as shown in FIG. 5, the solder 31 in a molten state adheres onto the conductor 7 on the inner wall surface of the groove-shaped recess 6 to thereby form a solder fillet 32, which electrically connects the electronic apparatus 10 to the external electrical circuit board 20.
The groove-shaped recesses 6 onto which the conductors 7 adhere are formed in the side surfaces of the insulating base 2, usually have a semicircular cross-section and a uniform inner diameter, and extend in the vertical direction. The connecting pads 5 usually have a rectangular shape and are arranged at regular intervals over the entire peripheral portion of the lower surface of the insulating base while one side of each connecting pad is in alignment with the edge of the lower surface of the insulating base (e.g., refer to Japanese Unexamined Patent Application Publication No. 2003-68921).